Reported August 2006

BACKGROUND: Perception and action -- the interactions between mind and body -- could be interlinked. Athletes often say that when they are playing well -- shooting hoops, hitting baseballs, catching football passes -- the ball appears bigger. When they are in a slump, the ball appears smaller. A new study by University of Virginia psychologists revealed a connection between batting averages of softball players and how big or small they thought the ball seemed.

ABOUT THE STUDY: The scientists conducted their experiment at several softball fields in Charlottesville, Virginia, and asked players who had finished playing for the day to look at eight different-sized circles on a board and to pick the one that best represented the size of the softball they were trying to hit. They compared that data to the hitting percentage of the players for that day. The study revealed when players were hitting well, they clearly perceived the ball to be bigger. And when they were hitting less well, they perceived the ball to be smaller. The scientists plan to continue their study on perceived ball size and batting averages under more controlled conditions.

HOW WE SEE "DEPTH:" The human visual system is designed to allow us to detect fine detail, track a moving object, see colors, and perceive depth. All these components of a visual scene are processed and merged by the brain so that we observe them as one visual experience. How we recognize that different objects are at different distances from us depends on visual cues. For objects beyond 100 feet, the image that's projected on to the back of the eye is basically the same size to both eyes, so cues of depth perception would include knowing the relative range of sizes of objects in general. If one object partly hides another, we know that the object in front is closer. And as we move our heads and bodies, nearby objects will seem to move more quickly than distant objects, an effect called motion parallax.

For objects closer than 100 feet, we need 3-D vision. Because the eyes are separated by about six centimeters, each eye gets a slightly different view of the same object. So when we fixate on one object, we can tell if another object is in front of or behind it, because the object is located in two different places on the images that reach the retinas, or backs of the eyes. This is called disparity. Experiments have found that depth perception likely occurs in the primary visual cortex, where individual neurons receiving input from the retinas of the two eyes fire specifically when retinal disparity exists.

VISION PROBLEMS: If particular parts of the brain are damaged, people may lose some visual perception. They might not be able to recognize faces, for instance (prosopagnosia), or not be able to name colors (color anomia). And sometimes they can lose their stereoscopic vision (visual spatial agnosia) or lose the ability to see objects that are in motion (movement agnosia).

If you would like more information, please contact:

Jessica Witt
Cognitive Psychology
University of Virginia
(434) 982-4744
jwitt@virginia.edu

FACTOID...

When Mickey Mantle hit a 565-foot home run, he claimed he "saw the ball as big as a grapefruit." But Joe Medwick of the St. Louis Cardinals claimed during a slump that he felt like he was "swinging at aspirins."